This invention relates generally to a multi-pole high-speed generator, and, more particularly, to an apparatus and method of having a pair of end caps on a rotor of the multi-pole high-speed generator for balancing the rotor and controlling concentricity and cooling during generator operation.
High-speed generators are used in many applications, including on gas turbine engines for aircraft, ships, and military vehicles. Such generators typically rotate at relatively high speeds (e.g., 12,000 r.p.m. to 24,000 r.p.m. or greater) during operation. While high-speed generators are generally safe and reliable, they may have drawbacks in certain circumstances. Large centrifugal forces may be imposed upon the generator""s rotating parts, such as the rotor. One such generator rotor has four poles, each of which is wound with wire conductors, called windings. During operation of the generator, the windings that rotate with the rotor are subjected to these relatively high centrifugal forces, which may cause the windings to separate from the rotor. The centrifugal forces may also cause the rotor to become improperly balanced and thus off-center as it spins during generator operation. Improper balancing of a rotor in particular can result in inefficiency in the operation of the generator, and may in extreme circumstances cause generator failure.
To secure the windings against such centrifugal forces, it is known to mount support wedges between each of the respective poles. Although these support wedges assist in containing the windings against the pole body so as to oppose the centrifugal force during rotation of the rotor, they too experience high centrifugal forces. The centrifugal forces may cause the support wedges to slip radially outward away from the shaft of the rotor, thus limiting the ability of the support wedges to secure the windings against the pole body. Particularly if the axial length of a conventional rotor is relatively large in comparison with its diameter, the centrifugal forces may cause significant radial deflection or flexure of the support wedges near the rotor""s axial midpoint.
In order to prevent the support wedges from slipping radially outward, a conventional rotor may use bands around the outer diameter of the rotor to retain the support wedges. In another conventional rotor, an xe2x80x9cunderwedgexe2x80x9d system may be employed in which the support wedges extend in their arc length all of the way between neighboring pole tips on the rotor and snap rings are then used to hold the support wedges in place relative to the poles.
These conventional structures for retaining support wedges in place on the rotor are limited in their effectiveness in high-speed generator applications. Both the bands used to retain the support wedges and the components of the underwedge systems (particularly the snap rings) also can suffer from bending from centrifugal forces and therefore may provide only a limited amount of counteracting force to keep the support wedges in place and may create an additional imbalance in the rotor. Additionally, because it is difficult to accurately control the positioning of, and the amount of pressure applied by the bands and underwedge componentry, it may be difficult to accurately set and maintain the positioning of the support wedges and to control the concentricity of the various support wedges around the rotors during operation of the generator. If the support wedges are not concentric (or evenly-spaced) about the rotor""s axis, then the spinning rotor assembly will be out of balance.
Also during operation of the generator, current passes through the wire windings, thereby generating heat. Some of this heat should be removed from the generator, particularly from the windings, to allow efficient operation of the generator and to keep the wire winding temperature below the point where the wire""s insulation begins to break down. If an insufficient amount of heat is removed from the generator, then the power output from the generator may be limited and the insulation of the wires within the generator may degrade. Conventional cooling systems such as air or limited conduction, or spray of the rotor core may, under certain circumstances, not offer sufficient heat dissipating capacity for the high speed generators.
Accordingly, there is a need for a novel rotor assembly and method that will permit a high-speed generator to work at optimum efficiency. There is also a need for a novel rotor assembly and method that will provide improved securing of support wedges on a rotor even at high speeds of operation so that the support wedges will continue to provide support for and direct pressure toward the generator windings. There also is an additional need for a novel rotor assembly and method that will accurately set and maintain the positioning of the support wedges and control the concentricity of the various support wedges mounted around the rotor during operation of the generator. There is an additional need for a novel rotor assembly and method that do not have components that have a tendency to increase rotor imbalance. There is a further need for a novel rotor assembly and method that substantially cool the generator during operation thereof. The present invention fulfills one or more of these needs and may provide other related advantages.
The present invention provides a multi-pole high-speed generator comprising, generally, a rotor assembly with a rotor having an end cap on each end for balancing the rotor and controlling concentricity and cooling thereof during generator operation. The method of cooling the generator using the end caps is also provided.
The rotor includes a plurality of poles that extend radially away from the shaft, each of which is wound with conductors, called windings. The rotor is defined by a generally cylindrical rotor body with a shaft extending axially through the rotor. The shaft includes a bore extending from a first end having an opening to a second closed end. Additionally, orifices extending radially from the bore are provided in a side wall of the shaft near the first and second ends thereof. The number of orifices at each end of the shaft corresponds to the number of poles.
A support wedge is mounted in the area between each of the respective poles. The support wedge may include an outer support wedge and an inner support wedge. The position of the outer support wedge is accurately set and restrained on the rotor by the end caps. A first and a second end of each of the outer support wedges include paired openings arranged either along an outer edge of the outer support wedge in the first embodiment or along the same radial line in an alternative embodiment. The first and second ends of the outer support wedges in the first embodiment may also include at least one supply port which is open to at least one axial channel in the outer support wedges for flow of a cooling medium, preferably oil.
The end caps comprise a substantially circular end wall circumferentially surrounded by an annular flange. The annular flange projects inwardly from the end wall toward the opposite end cap. The end caps include paired end cap openings with each pair at 90 degree angles to each other. In the first embodiment, the paired end cap openings are arranged circumferentially with a separate cooling medium feed port between the openings in each pair. In an alternative embodiment, the paired end cap openings may be arranged along the same radial line with at least one of the openings in each pair serving as the cooling medium feed port. The at least one of the openings in each pair may be slightly larger to effect this purpose. Each of the end caps also include a bore substantially in the center of the end wall and a raised peripheral edge having a plurality of circumferentially spaced openings provided therein for insertion of weights to help balance the rotor.
The end caps also include a manifold for circulating the cooling medium through the rotor. The manifold is at a hub location on the interior of each end cap. The manifold includes an annulus at an inner face of the bore and cooling medium galleries that extend radially away from the annulus toward an inner surface of the flange. The cooling medium galleries are each capped by a plug at an outer surface of the flange. The number of cooling medium galleries in each end cap corresponds to the number of support wedges. The end caps and/or the outer support wedges may include a groove for a sealing member between the end caps and the outer support wedges.
To assemble the rotor, the end caps are positioned on the respective ends of the rotor body with the bore centered around the shaft to substantially maintain rotor centerline control during generator operation. The annular flange extends circumferentially around the axial ends of the rotor body including the axial ends of the outer support wedges to help restrain them against the windings. After being machined to provide close tolerance fits, the ends of the outer support wedges are substantially centered under the inside of each flange. In the first embodiment, the separate cooling medium feed port in the end caps are mated with the at least one supply port in the first and second ends of the outer support wedges. The paired end cap openings are mated with the paired openings in the first and second ends of the outer support wedges. Axial screws are inserted into the paired end cap openings and then into the corresponding paired openings in the ends of the outer support wedges. In the alternative embodiment, this means that at least one of the end cap openings in each pair serves as both the cooling medium feed port and receives the axial screws and at least one of the paired openings in the first and second ends of the other support wedges serves as the supply port and receives the axial screws.
The bore and the annular flange are shrunk fit respectively around the shaft and over the axial ends of the outer support wedges. Thus, the end caps are shrunk fit both between the shaft at an end cap inner diameter and the outer support wedges at an end cap outer diameter. The end caps seal the rotor ends and restrain the support wedges tightly against the windings. When the end caps are disposed over a first and second end of the rotor body, each of the cooling medium galleries in the end caps radially extend from one of the orifices in the shaft to the at least one supply port in each end of the outer support wedges. The first end of the rotor body is the anti-drive end, and the second end of the rotor body is the drive end.
During operation of the generator, the cooling medium flows into the first end of the shaft, exits the shaft radially out the orifices at a second end of the shaft, through the annulus to the cooling medium galleries in the end cap at the second end of the rotor body, into at least one feed port into that end cap and into the at least one supply port in the second end of each of the outer support wedges, through the axial channels of the outer support wedges extracting heat, then out the at least one supply port at the first end of each of the outer support wedges, through the radial cooling medium galleries of the end cap at the first end of the rotor body, out the annulus of that end cap and into the orifices at the first end of the shaft for exiting out the open first end of the shaft and removing heat from the rotor.
Other features and advantages of the present invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.